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Constant Ratio Of Airborne To Absorbed CO2 In Carbon Cycle May Indicate Resilient Carbon Sinks

by Jack Rosebro

Airborne fraction
Total anthropogenic emissions (thick solid line) and amount of total emissions (46%) remaining in the atmosphere as the airborne fraction (thick dashed line). Thinner lines represent observed atmospheric CO2 increase derived from direct measurements, taking the average of Mauna Loa (Hawaii) and the South Pole (thin solid line), and two ice cores: Law Dome (dashed thin line) and Siple (dotted thin line). Source: Wolfgang Knorr, Bristol University. Click to enlarge.

A new analysis of anthropogenic emissions as well as atmospheric concentrations of carbon dioxide from 1850 to the present day indicates that the relationship known as the “airborne fraction”—the ratio of manmade CO2 emissions to the amount of those emissions that remain in the Earth’s atmosphere—has remained remarkably constant throughout the years, varying by an average of 0.7% ± 1.4% per decade. The analysis indicates that natural carbon sinks are maintaining overall resilience despite recent signs that the carbon uptakes of specific sinks are in decline.

The study, which was conducted by Wolfgang Knorr of the University of Bristol, UK, may have implications for upcoming climate negotiations, particularly with regard to deforestation and other land-use changes.

Approximately 40-45% of carbon emissions emitted every year remain in the atmosphere, with the balance absorbed as part of the Earth’s carbon cycle. Many projections of future greenhouse gas (GHG) emissions and subsequent warming trends, particularly those used by the United Nations Framework Convention on Climate Change (UNFCCC), assume a constant airborne fraction to 2100.

However, research published after the 2007 release of the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), which incorporates projections utilized by the UNFCCC, has shown a decline in specific carbon sinks such as the Southern Ocean. (Earlier post.) With newer climate-carbon cycle coupled models suggesting that a weakening of carbon sinks could add as much as net ~500 ppm carbon dioxide to the Earth’s atmosphere by 2100, concerns have been raised as to whether a relatively flat airborne fraction should be assumed for the remainder of the century.

While some aspects of the Earth’s “carbon budget” (e.g. annual increases of manmade emissions of carbon dioxide, concentrations of the gas in the Earth’s atmosphere, and the resultant uptake of carbon by natural sinks) have been relatively straightforward to calculate, quantifying the precise mechanisms by which carbon is naturally stored has proved more difficult. One knowledge gap is the so-called “missing carbon sink”, a phenomenon that has been studied extensively for the past three decades.

Carbon Flux
Estimated carbon emissions and uptake, 1850-2000, including the Earth’s as yet unidentified carbon sink. Source: Woods Hole Research Center Click to enlarge.

For example, one estimate from the Woods Hole Research Center calculates the average annual emissions of 8.5 petagrams of carbon (PgC) during the 1990s (about three-fourths from combustion of fossil fuels and the remainder from changes in land use). With the sum of the annual accumulation of carbon in the atmosphere and the annual uptake by the oceans calculated at 5.6 PgC, an additional sink of 2.9 PgC per year exists, but cannot be accounted for.

A systematic decline in the Earth’s ability to absorb steadily increasing carbon emissions would have the net effect of forcing the increase of atmospheric greenhouse gas concentrations at a rate sharply higher than models currently project. Although most climate models do not calculate the effects of “positive feedbacks”—secondary effects of increased GHG emissions which, in turn, intensify the severity and rate of warming—efforts are underway to develop more complex models that incorporate feedback effects. A lack of accounting for feedback effects is considered to be a potential weakness of many current climate models.

However, Knorr focused on observational data, analyzing atmospheric concentrations of carbon dioxide recorded at Mauna Loa, Hawaii and the South Pole. Ice core data from Law Dome, East Antarctica was used to determine concentrations of carbon dioxide prior to instrumental records. Data on worldwide CO2 emissions from fossil fuel combustion, cement manufacturing, and gas flaring, as well as carbon flux to the atmosphere resulting from land-use changes, were provided by Oak Ridge National Laboratories.

Another concern has been the influence of land use changes on carbon uptake in tropical forests, which are generally not monitored as well as northern forests. In the absence of observational data, researchers have had to rely more heavily on climate-coupled computer models of land-use changes, with significant margins of error. Knorr found that “the statistical model of a constant airborne fraction agrees best with the available data if emissions from land use change are scaled down to 82% or less of their original estimates.”

Knorr’s data does “not necessarily” run counter to theories of weakening carbon sinks, cautions the author. “Like all studies of this kind”, he notes, “there are uncertainties in the data, so rather than relying on nature to provide a free service, soaking up our waste carbon, we need to ascertain why the proportion being absorbed has not changed.”


  • Knorr, W. (2009), Is the airborne fraction of anthropogenic CO2 emissions increasing?, Geophys. Res. Lett., 36, L21710, doi: 10.1029/2009GL040613



If this is not approved by IPCC and CRU I refuse to believe in it.

Will S

Since this is on par with current climate models, it makes no impact on model projections. No 'approval' necessary.


Will, I can't speak for Raymond, but I think you are missing the point. The CRU has been revealed to be disingenuously stating that there were no peer reviewed articles that did not support anthopogenic global warming, then it is shown that they were actively suppressing those very articles. CRU was using a trick to eliminate a trend line that went against their chosen outcome, and the CRU was refusing to release their data so that other scientific groups could verify and duplicate their results. And then the lead CRU investigator stated that if a FOI act request was made that he would delete the data. The British equivalent of an FOI request was made, and voila, the data was found to be accidentally deleted. The IPCC says that if CRU was cooking the books we aren't to worry because their other sources were finding the same results, but they won't release their data either. And these other sources tend to have guys like Mann (the originator of the infamous, fabricated, hockeystick graph) in them as well. And the guy that was collating the data came out and stated that it was getting close to the garbage in, garbage out stage. It is obvious that the global temperatures are higher now than they were a century ago, but cooler than they were in the medieval warm period, but even there the IPCC and the CRU are trying to eliminate the consensus on a historic event. I don't doubt that CO2 levels affect global warming, perhaps they are even a significant fraction of the warming done by water vapor, or methane, but we don't know because the science so far has been done in a non-scientific manner.
The IPCC and the CRU have no credibility on global warming, we need to find a group that will use publicly acknowledged numbers and some semblance of the scientific model, as opposed to the CRU rush to judgement.

The IPCC and the CRU have no credibility on global warming,
Yeah right! Thank God we have Fox Noise to set us right.

Dursun, do you approve of the way the science has been handled by the CRU and the IPCC? It is incredible that these people are the ones we have to rely on regarding an issue that could cost the world billions of dollars. I don't watch Fox, but I doubt that they are as far from the truth on this issue as the CRU is.

Stan Peterson

Since the skeptics started questioning them in earnest, and Climategate scandals hit, the AGW warmist hysterics have been seeking any finding to buttress their collapsing thesis. They have proposed that the natural sequestrations are becoming saturated, for one.

This is utter bilge since the oceans sequestration is some 70 times all the CO2 in the atmosphere, in just the first 100 meters of ocean depth. Expecting a CO2 change by 2100, of about 1/2000th of the trace amount in the atmosphere, will somehow not continue to be absorbed is ridiculous on the face.

Just as another proposition ha been advanced that a 1/2000th change in a 1/70th portion of the carbon in the seas, will alter the alkalinity in any measurable way is also absurd. it would supposedly harm corals. But corals evolved in an era when atmospheric CO2 was a substantial portion of the atmosphere and not a reduced to a trace gas.

It is appropriate that new scientific evidence analyzing the ratios of 12CO2, 13CO2, and 14CO2, the common and a few rare isotopes of Carbon, has proven that the 'missing reservoir' doesn't exist. It is so needed by hysteric climategater Solomon and others to maintain the fiction that CO2 is resident for thousands of years.

The IPCC will now have to admit that the average residence time of CO2 in the atmosphere is but 5 years and not the one-way trap door that Soloman and her associates, posit will give CO2 residence time of as many years as they need, to produce the AGW answers that they seek.

In the IPCC AR4, the IPCC noted that it will return to the Henry's Law residence times, if the AGW hysterics cannot find their 'missing reservoir'. This cuts the CO2 AGW problem by the direct ratios of of their residence times. Most AGW hysterics currently postulate 300 years of residence time, so the cut in CO2 direct effect is 300/5 or 60 times.


One need only read the Telegraph's recent article on IPCC Chair Pachauri and the myriad businesses he runs, to understand the corruption there. Follow the AGW money right to the IPCC Chair's pocket.


The skeptics are going to jump all over this and site it as absolute "proof" that AGW is a hoax.
The earth's climate is a vastly complex system. 'System' may not even be the appropriate word, since there may be many random inputs (like variations in the suns radiation) that we have little knowledge of.
I have always felt it is better to err on the side of caution than to recklessly continue behaving in a way that might endanger our species, even if it impacts the world economy negatively, in the short term.
My uncle smoked 2 packs of unfiltered Camel cigarettes every day and lived to be 89. I however choose not to take that chance and don't smoke.


danm, it is disingenuous to compare IPCC claims to AGW theory and smoking. Here's why:

90 percent of all the ice on Earth resides in the Antarctic. Ninety percent. Sea ice extent and area are a reasonable indicator of a "global warming" signal. Both Antarctic sea ice extent and area have increased since the start of satellite records.

Ten years of peer review study confirm this. Carbon trading schemes and GHG regulations do nothing to protect the environment - they do enrich a select few people and organizations. The cancer here is from the AGW theory - not CO2.


It appears that GCC is engaging in censorship as my previous post pointing out the folly of the AGW deniers' logic has been removed. I will not repost.


"90 percent of all the ice on Earth resides in the Antarctic. Ninety percent. Sea ice extent and area are a reasonable indicator of a "global warming" signal. Both Antarctic sea ice extent and area have increased since the start of satellite records. "

References please.

The above paragraph is highly misleading. Notice how he starts off by saying that 90% of the world's ice is in Antarctica (referring to the land ice on the continent), but then skillfully and silently switches over to talking about sea ice?

Antarctic sea ice extent has little relevance compared with arctic sea ice extent since there is none in summer, it all melts every year anyways. I notice how you conveniently neglected to mention the dramatic decline in arctic sea ice extent over the last few decades. I guess that's because you are biased and cherry pick which data you will ignore vs. promote.

Data which shows Antarctic sea ice (purportedly) increasing is worthy of mention. Data which shows Arctic sea ice dramatically shrinking is not worthy of mention.


Mark, it looks like you hit a database glitch or had something held for moderation.

Ziv, do you know what the "trick" was about?  It was using temperature readings instead of tree-ring proxies after 1960, because rising CO2 changed the relationship between higher temperatures/drought conditions and tree growth after that.

People who go on about the "trick" being some nefarious thing show they have fully bought into the propaganda.  If you claim your position is based on the data, you can't use sound-bites like this... and you can't trust anything from the people who stole and published them, either.


Once again someone has used Antarctica's ice gain as proof AGW isn't real when in fact it's more likely that it's another sign AGW is real. How so? Well if the continental ice sheet is growing where's all the ice water coming from?

Antarctica is one of the dryest places on Earth; for the ice sheet to be growing at the rate it is the climate has to have changed. GW causes water to evaporate from the world's oceans. That water doesn't stay in the air for long, it comdenses whenever it gets cold enough and Antarctica is cold enough.

Antarctica is not just one of the dryest places on Earth it is also the coldest continent on Earth; it's so cold that even if the temperature rise we've seen were 10 fold greater it would still be cold enough for water to freeze out of the air.

Why Antarctica should be different from the Arctic, where the ice is melting, has everything to do with geography: Antarctica is a continent surrounded by water while the Arctic is an ocean enclosed by land but still linked to warmer oceans. It has to do with the Antarctic ice sheet making Antarctica the highest continent, which makes the air thinner and it has to do with the relative strength of the polar vortex around each pole; the south pole vortex goes around Antarctica and over water so it maintains its strength and keeps out warmer air while the north polar vortex travels over land which not only weakens it but also diverts it south to bring cold weather to warmer places.


"Mark, it looks like you hit a database glitch or had something held for moderation."

Yes I suppose I shouldn't be so cynical


EP, Jones was working on the WMO statement on the status of global climate in 1999 when he used the phrase 'Mikes Nature trick' referring to Jone's use of Mann's and Briffa's charts for early temperature trends as well as his own married up to instrument measured temps in a graph in which Jones uses two different dates (Mann used 1980 as the cutoff date and Jones used 1960 as the cutoff on Briffa's data) to shape the data to make the graph look like the temperature trends were markedly turning to the hotter end of the scale when if the data hadn't been massaged the graph looks decidedly less alarming. This kind of manipulation of data is sometimes necessary when you are dealing with multiple sources of temperature proxies, but you have to be able to see the data in order for the science to be relied on, which is the scientific method itself.
My professors at University used to lecture at length on the importance of full disclosure of data so that their peers could verify the validity of their conclusions. This is the most important science of our generation and the very essence of the scientific method has been thrown out the window. I don't deny that the temperatures have gone up over the past 100 years, but if the AGW backers want to convince me that they are right it being caused by human carbon emissions, they need to do the science right, not hide behind secret data, manipulated charts and tricks.
If you can't look at the emails and see the obvious problems they bring to the CRU and the IPCC, you are not paying attention.



"Will, I can't speak for Raymond, but I think you are missing the point."

Actually, Will is spot on. Raymond had missed the point of the conclusions in the paper that is the subject of the article. Will was gently pointing that out.

"The CRU..."

Let me stop you right there. Neither the article nor the paper discuss the CRU, and the IPCC is mentioned only peripherally. Curiously, you haven't even mentioned the paper cited in the article upon which you are supposedly commenting.

And keep in mind that if the IPCC is at fault for using the convention that the airborne fraction is relatively steady, then that would indicate that anthropogenic warming will come harder and faster than current models project.

Somehow, I don't think you intended to arrive at that result. It really does pay to read the source material before posting an opinion on the source material.

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